Plasma generation is useful for a variety of applications. For example, complex gas analyzers may excite a gas to cause the gas to emit energy at characteristic frequencies which may be analyzed. Also, in semiconductor fabrication, plasma may be used for etching, resist removal, passivation and deposition. Other applications include miniature chemical sensors, miniature ion beams, and information displays derived from addressable arrays of miniature plasmas.
Large scale, planar inductively coupled plasmas have a high degree of efficiency, as measured in eV per electron-pair created, as well as low cost and lack of complexity. Also, the electrodeless operation of the inductively coupled plasma generators allow continuous operation in reactive and corrosive environments. However, the size of typical inductively coupled plasmas are 10-100 cm and constructed from discrete components. These dimensions and design parameters limit the types of applications for these devices.
Currently available small-scale plasma technologies have several disadvantages. For example, corona discharges require extremely high electrode voltages that are not compatible with small scale lengths due to electrical breakdown. Also, the electrodes are subject to contamination and erosion due to the high energy plasma. In another example, capacitive alternating current discharges, which are used in inert gas plasma displays, include electrodes coated with a thin film which exhibits a high secondary electron yield, thereby allowing plasma generation at relatively low voltages. However, the film is contaminated and ineffective in a reactive gas environment. Also, plasma generation efficiency is low in these devices. An additional disadvantage of conventional small-scale plasma technologies is the significant fabrication cost associated therewith.
One example of plasma generation is found in U.S. Pat. No. 5,280,154 to Cuomo et al. disclosing a plasma processing apparatus having many discrete components that applies radio frequency energy to a nine inch square, 0.75 inch thick coil wherein a wafer is positioned 6-15 cm from the coil. In U.S. Pat. No. 4,948,548 to Ogle, a method and apparatus is described for producing uniform plasmas over a wide area by inducing a current in a coil to produce a magnetic field within an enclosure having a wafer therein. Ogle discloses coils having diameters from 8 to 20 cm.
It would be desirable to provide a microelectrical mechanical system (MEMS) plasma generator that is compatible with integrated electronics, operates at relatively low temperatures and voltages, is efficient, has a broad gas pressure range, has scale lengths in the order of millimeters, is inexpensive to manufacture, and is of planar geometry.